Organic EL devices have charge-transporting thin films formed from organic compounds which function as light emitting layers and charge-injecting layers. Particularly, a hole injection layer is responsible for transferring charges between an anode and a hole-transporting layer or a light emitting layer, and thus plays an important role in organic EL devices to work at a low voltage and achieve a high luminance.
The hole injection layer is produced by either dry processes (typified by vapor deposition) or wet processes (typified by spin coating). Comparing these processes, wet processes are superior to the dry process in ability to efficiently produce a flat thin film with a large area. Thus, there is an increasing demand for the hole injection layer that can be produced by wet processes in view of the fact that organic EL displays are evolving into one with a larger screen area than before.
With the above in mind, the present inventors have been engaged in the development of various charge-transporting materials which are applicable to a variety of wet processes and which give rise to outstanding thin films for hole injection layers of organic EL devices. The present inventors also have developed new compounds highly dissolvable in organic solvents and new charge transporting varnishes. (See Patent Documents 1 to 4.)